1. Field of the Invention
This invention relates to a magnetic disk medium quality control method and, more particularly, to a magnetic medium transfer quality control device that detects abnormal conditions in a magnetic disk medium, which stores servo information required for controlling a head position of a magnetic disk device, in a magnetic transfer process.
2. Description of Related Art
A magnetic disk device is widely used as a storage device for storing a variety of digital data and comprises a magnetic disk and a magnetic head. The magnetic head stores and regenerates data on and from the magnetic disk. The magnetic disk must perform a servo operation, in which the head is moved to a desired track so as to read out a desired recording track, and is positioned at a center of the track. This servo operation stores a servo pattern, which is used for acquiring data about the position of the head, on the magnetic disk. Normally, a device called a servo writer writes this servo pattern after a magnetic disk device manufacturer assembles a magnetic disk, a magnetic head, and the like, in one body. The servo writer writes the servo pattern by gradually moving the head from outside. Recently, however, storage capacities of magnetic disk devices have been rapidly increasing. Accordingly, the number of tracks in the disk device has also been increasing. This increases the period of time required for writing the servo pattern and results in increasing manufacturing costs for the disk device.
To address this problem, there have been developed methods of writing the servo pattern by magnetic transfer. In one example of known methods, a so-called master disk, in which a servo pattern has already been written, is adhered to a magnetic disk from which the servo pattern has already been erased. In another example, a master disk in which a pattern is structurally formed by a ferromagnetic substance is adhered to a magnetic disk, and a magnetic field is applied to the magnetic disk from outside of the master disk.
Although a disk device manufacturer can perform the magnetic transfer process, it is preferable for a magnetic disk medium manufacturer to perform the magnetic transfer process in a single step of the magnetic disk manufacturing process, because the disk is only used before it is incorporated into a disk device and thus requires a clean room. Hereinafter, a disk that is subjected to magnetic transfer in the magnetic transfer process will be called a transfer disk. A transfer disk used as a magnetic disk product in which a servo signal is normally written by magnetic transfer will be called a magnetic transfer disk.
If such a magnetic transfer process is incorporated into the medium manufacturing process, there is a problem in testing the medium. The problem will be described hereinbelow.
FIG. 4 shows an example of a typical manufacturing process after a magnetic film has been formed on a magnetic disk, in which the magnetic transfer has not yet been performed. In this example, a magnetic film is formed by sputtering, and a lubricant is then coated thereon (refer to step 1 and step 2). A tape cleaning is performed so as to remove particles on a surface (refer to step 3), and a total test is finally conducted. The testing process comprises a glide height test (refer to step 4), a read/write test (refer to step 5), and a visual test (refer to step 6). In the glide height test, it is determined whether there is such a bump as to interfere with the head provided with a piezoelectric element when the head is being used. In the read/write test, the number of defects present on a disk is determined by writing and reading a signal in or from the disk, using the same head as in the disk device. In the visual test, the presence of any scratches or pits in the surface of the disk is determined visually or by using an optical testing device. These testing processes assure the quality of shipped products, because nothing touches the recording surfaces of disks during these processes, since they are typically performed at the final stage of the medium manufacturing process.
On the other hand, FIG. 5 shows an example of a manufacturing process after a magnetic film has been formed on a magnetic disk in the case in which a magnetic transfer process is added. If the read/write test is conducted after the magnetic transfer process, the servo pattern written by the magnetic transfer will be erased. To solve this problem, the read/write test (refer to S5) must be conducted prior to magnetic transfer (refer to S7). The glide height test does not have to be conducted prior to the magnetic transfer, but if the glide height test is not conducted prior to the read/write test, the read/write test will be conducted when the disk has a bump that will interfere with the head, which is the glide height defect. This increases the number of damaged test heads occurring during the read/write test, and results in increased testing costs. Moreover, a single testing device conducts both the glide height test and the read/write test in many cases. For these reasons, the glide height test and the read/write test has been advantageously conducted prior to the magnetic transfer process, as shown in FIG. 5. However, since a servo pattern written by the magnetic transfer is not erased during the visual test (refer to S8), the visual test may be performed at the final stage after the magnetic transfer process.
In the magnetic transfer process as stated above, the master disk adheres to the magnetic disk to be manufactured (the transfer disk). This sometimes causes damage to the surface of the transfer disk, and this damage to the disk may affect the read/write action. Particularly if particles are introduced into the space between the master disk and the transfer disk during the magnetic transfer process, the distance between the master disk and the transfer disk is increased in the area immediately surrounding the introduced particles. This may inhibit the magnetic transfer signal from being normally recorded. Further, the particles may cause damage to the master disk and the transfer disk.
To avoid this problem, whether any particles are being introduced onto the transfer disk is preferably determined in a test for particles (refer to S6) just prior to magnetic transfer. In an example of this test for particles the disk is irradiated with a laser beam, so as to identify any particles introduced onto the disk by the presence of scattered light. In this method, however, it is impossible to completely prevent the introduction of particles, which are adhered to the disk between the test for particles and the magnetic transfer, particularly the fine particles that have escaped detection by the test for particles, which accumulate on the master disk and become larger particles.
If the particles adhere to the master disk as described above, the transfer disks made thereafter are unsatisfactorily manufactured by the magnetic transfer process. Further, since the read/write test cannot be conducted after the magnetic transfer process, as described above, the read/write test cannot assure the quality of the magnetic transfer disk. It would therefore desirable to provide a device to assure the quality of the magnetic transfer disk.
A magnetic transfer quality control device is provided to assure the quality of a magnetic transfer disk. In a preferred embodiment, the device includes a first read/write testing mechanism provided at the front section of a magnetic transfer device, the first read/write testing mechanism conducting a glide height test and a read/write test, a test for particles testing mechanism; an optical surface testing mechanism provided at the rear section of the magnetic transfer device; a second read/write testing mechanism for conducting a sampling glide height test and a sampling read/write test; an information collecting mechanism for collecting at least one of test results obtained by the respective testing mechanism; and a determination mechanism for making a predetermined determination according to the collected information about the test results to determine whether there are any abnormal conditions in the magnetic transfer process.
The most serious problem occurring in the magnetic transfer process is that the consecutive disks are made defective due to the particles adhering to the master disk or introduced into the space between the master disk and the transfer disk. The resulting damage on the transfer disk can be detected by optical testing after the magnetic transfer. Thus, an optical testing device monitors whether a plurality of consecutive transfer disks is defective or not. If yes, a warning, for example, an alarm, is given.
If the particles introduced into the space between the master disk and the transfer disk cause only a minor damage, this does not necessarily cause a problem to occur in operating the disk device. If the optical testing device determines that the transfer disk is defective due to such a minor defect, the ratio of non-defectives to defectives is lowered. To address this problem, the results of the sampling glide height test and read/write test are compared with the results of the optical test, so as to check whether the defects are located at the same position or not. Whether the standards for the optical test should be stricter or more flexible may determined according to the previous results of the checking process.
However, the greatest cause for particles to be introduced into the space between the master disk and the transfer disk is that particles sometimes adhere to the transfer disk being subjected to the magnetic transfer step. To prevent this, a test for particles is conducted before the magnetic transfer process as stated above. It is, however, impossible to detect all defects, including those caused by fine particles, and to remove any transfer disks to which such fine particles have adhered. Ordinarily, if the ratio of non-defectives to defectives in the test for particles is low, a greater proportion of particle-associated damage is being eliminated by the test for particles. It is therefore important to give an alarm when the ratio of non-defectives in the test for particles becomes lower than a predetermined value.
According to the present invention, one or more of above-mentioned methods are used to assure a desired quality of the magnetic transfer disk being manufactured.